The present invention is related to protection circuits for communication networks. More specifically, the present invention is related to a protection switch to support the redundant application of electrical and optical signal converters.
Fiberoptic communication networks are capable of carrying tremendous volumes of voice and data traffic. Businesses and individuals rely more and more on voice and data communications and are therefore becoming more heavily impacted by failure in communications equipment. In a fiberoptic network, optical fibers can become damaged or severed, and lasers can fail. Further, repeater equipment, and electrical and optical converter equipment, among others, are also sources of failure. Therefore, in order to increase the reliability of communication networks, backup systems have been developed. Protection channels are known in the art and are described, for example, in the U.S. Pat. No. 4,451,916 to Casper et al. Disadvantageously, Casper requires a twisted pair copper wire link coupled along the end terminal stations and each repeater station along the network for the purpose of monitoring and fault isolation in the event of a failure. Other protection schemes have been devised for high-speed data networks which require sophisticated add-drop multiplexing equipment to monitor the content of the signals being transmitted.
Typically, at either end of the fiberoptic network, signal converting equipment converts optical signals into electrical signals which can then be further processed to pull individual multiplexed data channels from a high-speed signal. It would be advantageous to provide multiple optical-to-electrical converter units at either end of multiple optical fibers to provide a redundant fiberoptic network. Thus, if one set of fibers failed, or if one signal converter unit at either end of an optical fiber failed, a backup path could be placed into service. Therefore, it would be desirable to provide a simple mechanism for automatically switching between redundant fiberoptic paths through multiple signal converting units.
The above described disadvantages are overcome and other advantages are realized by providing a network switch for connecting redundant signal converting devices to a communications port. The signal converting devices preferably convert optical signals to electrical signals for downstream transmission to subscriber equipment, and electrical signals from subscriber equipment to optical signals for upstream transmission. When the switch is in a first state, electrical signals from the first signal converting device are connected to the communication port. When the switch is in a second state, electrical signals from the second signal converting device are connected to the communication port. The network switch monitors alarm contacts of both signal converting devices, as well as the nominal current drawn by each signal converting device. If the alarm contacts are activated for the active signal converting device, or if the nominal current drawn by the active signal converting device stops, the network switch switches to the second state. The network switch also terminates power to the active signal converting device temporarily, to force an alarm condition at the far end, causing a corresponding remote network switch to switch to the corresponding backup signal converting device.
According to a further aspect of the invention, the network switch provides output alarm contacts, and closes a relay between the output alarm contacts if the alarm contacts associated with the first signal converting device are closed.
According to another aspect of the invention, a method of providing backup communications is described. Two signal converting devices are provided, which preferably each convert optical signals to electrical signals. The electrical signals from each signal converting device are connected to a network switch, which in turn can switch between a first state, in which the electrical signals from the first signal converting device are connected to a communication port, and a second state in which the electrical signals from the second signal converting device are connected to the communication port. The method further includes monitoring the alarm contacts associated with the first signal converting device, as well as measuring the nominal current drawn by the first signal converting device. If an alarm is detected, or if the nominal current decreases substantially, the method includes removing power from the first signal converting device temporarily, and switching to the second state, so that the electrical signals from the second signal converting device are connected to the communication port.
According to yet another aspect of the invention, the above method further includes closing output alarm contacts if an alarm is detected in the alarm contacts associated with the first signal converting device.